WRITTEN BY AISLINN SARNACKI
Of the many anticipated signs of spring in Maine, the return of ospreys is among the most easily observed. Flying up from their wintering grounds in the south, these fish-eating raptors build large, conspicuous stick nests atop trees, telephone poles, dock pilings, and other tall structures.
Apparently they don’t mind standing out, and they’re fun to watch.
“Their hunting skills are really impressive,” said Erynn Call, raptor biologist for the Maine Department of Inland Fisheries and Wildlife.
Hovering high over the water, ospreys will spot a fish, dive feet first, plunge into the water, and grab it.
“They can see something below the surface of the water even if they’re 100 feet up,” said Chris DeSorbo, director of Biodiversity Research Institute’s raptor program. “It’s like binocular vision.”
Unlike Maine’s other hawk species, they’ll submerge to grab a fish. But water doesn’t slow them down much. Resurfacing, they immediately take flight, shaking the water from their feathers as they rise.
Their accuracy is startling. Studies have recorded ospreys catching fish at least one in every four dives, with success rates sometimes as high as 70 percent, according to the Cornell Lab of Ornithology.
The average time ospreys spend hunting before making a catch? Just 12 minutes.
They’re a bird that’s built to fish — right down to their feet. Unusual among hawks, they possess a reversible outer toe that allows them to grab a fish with two toes in front and two behind. Barbed pads on the soles of their feet also help them secure their quarry.
“You’ll see that their feet have this amazing scaly, sandpaper texture, which is pretty helpful when trying to hold onto a slippery fish,” DeSorbo said.
Today, the osprey is a common sight in Maine, but they weren’t always so numerous. Back in the 1950s and 60s, bird populations throughout the United States plummeted due to the use of pesticides such as DDT, which caused eggshells to thin and break.
“Ospreys were one of the species that helped people figure out that DDT was having the devastating effect on birds that it was,” DeSorbo said, explaining that because the bird nests in such visible locations, it’s easy for scientists to monitor them.
Since the ban of DDT in 1972, ospreys and other birds, including bald eagles, have rebounded. Today, Maine’s osprey population appears to be stable based on surveys conducted in Casco Bay, said DeSorbo and Call.
Pairs return to the same nesting sites year after year, and their young tend to nest nearby. Males collect most of the nesting material, while females arrange it. Over time, a nest can grow to be over 10 feet deep and 6 feet in diameter — big enough for a person to sit in — according to the Cornell Lab of Ornithology.
The osprey is tied to other birds in interesting and unexpected ways. For example, smaller birds, such as common grackles , sometimes nest in the lower parts of active osprey nests, according to Mary Holland in the book “Naturally Curious.”
In Maine specifically, ospreys have been observed nesting within heron colonies, Call said, and peregrine falcons sometimes use old osprey nests. But perhaps the osprey’s greatest tie to another species is to the bald eagle — which basically serves as its archenemy. Bald eagles are often witnessed stealing ospreys’ fish by harassing them in the sky.
“They’ll basically pester them until they’re too tired to continue on, and then they’ll drop the fish,” DeSorbo said. “Often eagles will catch it from the air before it even hits the water.”
If observing a pair of nesting ospreys this spring, keep an eye out for one to three chicks. Both adults will feed them, carrying fish back to the nest — with the fish always oriented head first to reduce wind resistance.
It takes about two months for baby ospreys to fledge, but they continue to call the nest home until they migrate south in the fall. Then they’ll travel as far as central South America.
If you’re interested in building an osprey nesting platform or you’d like to participate in monitoring them, visit osprey-watch.org. OspreyWatch is a global community of people who report breeding data for more than 8,800 osprey nests worldwide.
And if you’d just like to watch osprey fish, Call suggests visiting places where you can observe alewives run upriver in the spring, such as the Damariscotta Mills Fish Ladder. There you’ll likely see several ospreys, eager to snatch up a fish and carry it away.